MPH vs HRM. Best way to lose weight question.

Asiral

So, since I was pretty sick yesterday, I wanted to work out but take it easy. I use an elliptical that has a polar HRM on the handles. I stayed at a steady 4 mph for the majority of my workout. The HRM read 157 for the most part. (I am an overweight short female.)

My question is this... Is it better to go at a slower pace and workout for a longer period of time, or workout at a higher pace? I notice it was easier for me to stay steady at 4mph. But at 6 mph, I cant hold that speed consistantly and im way out of breath. I sweat about the same honestly. Maybe it just comes down to what works best for you personally? Id love to hear your opinions! Thanks!
~Asiral